Multi-vector sensing in cardiac devices with signal combinations

ABSTRACT

Methods and devices for combining multiple signals from multiple sensing vectors for use in wearable or implantable cardiac devices. Signals from multiple vectors may be combined using weighting factors and/or by conversion to different coordinate systems than the original inputs, which may or may not be normalized to patient anatomy. Signals from multiple sensing vectors may be combined prior to or after several analytical steps or processes including before or after filtering, and before or after cardiac cycle detection. Cardiac cycle detection information may be combined across multiple sensing vectors before or after analysis of individual vectors for noise or overdetection. Cardiac cycle detection information may also be combined across multiple sensing vectors to identify noise and/or overdetection.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of and priority to U.S.Provisional Patent Application Ser. No. 62/245,757, titled SIGNALQUALITY MONITORING FOR MULTIPLE SENSE VECTORS IN CARDIAC DEVICES, U.S.Provisional Patent Application Ser. No. 62/245,738, titled MULTI-VECTORSENSING IN CARDIAC DEVICES WITH SIGNAL COMBINATIONS, U.S. ProvisionalPatent Application Ser. No. 62/245,762, titled MULTI-VECTOR SENSING INCARDIAC DEVICES WITH DETECTION COMBINATIONS, and U.S. Provisional PatentApplication Ser. No. 62/245,729, titled MULTI-VECTOR SENSING IN CARDIACDEVICES USING A HYBRID APPROACH, each filed on Oct. 23, 2015, thedisclosures of which are incorporated herein by reference.

BACKGROUND

A number of cardiac rhythm management products are available for the usein diagnosis and treatment of various conditions. These may include, forexample, subcutaneous, transvenous, or intracardiac therapy devices suchas pacemakers, defibrillators and resynchronization devices.Implantable, external and/or wearable cardiac monitors are alsoavailable. External or wearable therapy products may includedefibrillator vests and external pacemakers, as well as automaticexternal defibrillators.

In some cardiac rhythm management products, a plurality of sensingelectrodes may be provided for use in obtaining cardiac electricalsignals for analysis of the patient's cardiac status. Some such productshave sufficient sensing electrodes to define more than one sensingvector, with each sensing vector defined by a combination of 2 or moreelectrodes. Some devices select a primary sensing vector as the “best”vector for use in observing cardiac conditions. It may be useful toinstead use data from multiple vectors simultaneously. New andalternative approaches to the use of data from multiple sensing vectorsare desirable.

OVERVIEW

The present inventors have recognized, among other things, that aproblem to be solved is the need for new and alternative approaches tothe use of multiple sensing vectors in cardiac devices. In someexamples, data from multiple vectors are combined together to generate acombined data stream. In other examples, data from multiple sensingvectors, and/or a combined data stream, are processed in parallelthrough portions of a cardiac signal analysis, with results of suchanalysis later being combined together. The point where the multipleparallel processing items come together varies in different examples. Inat least one example, data across the multiple parallel processes arecombined repeatedly while the parallel processes proceed forward.

This overview is intended to provide a summary of subject matter of thepresent patent application. It is not intended to provide an exclusiveor exhaustive explanation of the invention. The detailed description isincluded to provide further information about the present patentapplication.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, which are not necessarily drawn to scale, like numeralsmay describe similar components in different views. Like numerals havingdifferent letter suffixes may represent different instances of similarcomponents. The drawings illustrate generally, by way of example, butnot by way of limitation, various embodiments discussed in the presentdocument.

FIG. 1 shows an illustrative implantable medical device system withmultiple sensing vectors available;

FIG. 2 shows schematically an illustrative input circuit design;

FIG. 3-11 show illustrative methods in block flow form;

FIG. 12 includes representations of cardiac electrical signals along twosensing vectors and corresponding cardiac cycle detections todemonstrate an illustrative method;

FIGS. 13-15 show cardiac cycle detections in two channels forillustrative methods;

FIG. 16 illustrates a signal analysis method in which a signal isoverlaid and summed with a filtered version of itself;

FIGS. 17-20 show illustrative methods in block flow form;

FIG. 21 shows an implantable monitor; and

FIG. 22 illustrates a wearable cardiac rhythm management device.

DETAILED DESCRIPTION

FIG. 1 shows the S-ICD System™ from Cameron Health, Inc., and BostonScientific Corporation as implanted in a patient. The system isimplanted in a patient 10 with a canister 12 in the left axilla at aboutthe level of the cardiac apex. A lead 14 is placed subcutaneously,beneath the skin and over the ribcage of the patient, with a firstportion extending along the inframammary crease to the xiphoid, and thensuperiorly parallel to and about 1-2 cm to the left of the sternum. Aproximal sense electrode 16, shocking coil electrode 18, and distal tipsense electrode 20 are provided along the parasternal portion of thelead 14. The entire system is implanted outside of the ribcage.

The canister 12 may further include such components as would beappropriate for communication (such as RF communication, inductivetelemetry or other suitable communication linkage) with an externaldevice such as a programmer 22 or a bedside or home monitoring device.For example, during an implantation procedure, once the canister 12 andlead 14 are placed, the programmer 22 may be used to activate thecanister 12 and/or direct/observe diagnostic or operational tests. Afterimplantation, the programmer 22 may be used to non-invasively determinethe status and history of the implanted device. The programmer 22 incombination with the canister 12 may also allow annunciation ofstatistics, errors, history and potential problems to the user/medicalpractitioner, and may also allow for updating of programming in thecanister 12.

There several individual and combinational sensing vectors availablewith this implantation. In the commercial implementation there are threeavailable sensing vectors: between electrode 16 and electrode 20,between electrode 16 and the metal housing of the canister 12, andbetween electrode 20 and the metal housing of the canister 12. Ifdesired, the system could also be modified to use electrode 18 as asensing electrode, paired with any of electrodes 16 and 20 or the metalhousing of the canister 12. Moreover, it would be possible to combinetwo electrodes as a single pole for sensing, if desired.

The illustration in FIG. 1 is just one example. In additional examples,an implantable or wearable cardiac monitor may have multiple electrodeson a housing and/or lead to define two or more sensing vectors. Leadlessdevices, such as leadless cardiac pacemakers for implantation inside theheart, may have multiple sensing electrodes on or extending from acanister or housing to define multiple sensing vectors. Wearabledefibrillators or pacemakers may also provide multiple cutaneouselectrodes on the anterior and/or posterior thorax of the patient, andmay even include indifferent electrodes elsewhere such as on a limb.Additional sensing data may be mathematically derived from combinationsof the physical vectors provided by the sensing electrodes. Transvenousand/or epicardial implantable devices may have an active housing adaptedfor use in sensing along with plural electrodes for sensing on one ormore leads, as is well known in the art. For example, a transvenousdevice may have a right ventricular lead with atrial and ventricularsensing electrodes as well as an indifferent electrode on the canister.

For any of these systems, the availability of multiple sensing vectorsposes several questions, including how to determine which of severalsensing vectors is or is not performing well, and how to decide whetherto switch from one sensing configuration to another. The firstgeneration of the S-ICD System shown in FIG. 1 incorporated sensingvector selection methods in the clinical setting while in communicationwith a programmer. Some details of such methods are discussed in U.S.Pat. Nos. 7,392,085, 7,623,909, and 8,200,341, the disclosures of whichare incorporated herein by reference. The device did not automaticallyswitch sensing vectors in response to identified sensing signal qualitymetric changes.

Some additional background discussion of the use of multiple vectors andsensing therewith is shown in U.S. Pat. No. 5,313,953, as well as U.S.Pat. No. 5,331,966 which additionally shows a device with multiplehousing electrodes for sensing. While these prior discussions identifythe possibility of ambulatory vector quality monitoring and switching,and/or combining multiple sense vector signals together, there remainsadditional need for alternatives and new devices and methods to performsignal quality monitoring, sense vector switching, and/or to provide forcombining multiple sense vectors together. U.S. Provisional Application62/245,757, titled SIGNAL QUALITY MONITORING FOR MULTIPLE SENSE VECTORSIN CARDIAC DEVICES, the disclosure of which is incorporated herein byreference, discusses monitoring signal quality with various metrics aswell.

FIG. 2 shows an illustrative sensing input system. A plurality of analoginput channels are defined as indicated at 50. The analog channels 50may be dedicated or hard wired to a particular combination of sensingelectrodes, or may be defined using a multiplexor or other switch arrayto couple to pairs or groups of sensing electrodes such as describedabove and/or in association with FIG. 1. The individual channels mayinclude DC blocking, bandpass, notch, bandstop, 50/60 Hz blocking,and/or other filtering circuitry as well as amplification circuitry suchas a low noise amplifier, either as stand-alone circuits or operatingcooperatively with an analog to digital conversion (ADC) circuitry 60.Any suitable ADC circuitry may be used, including a wide array of suchdevices known in the art including delta-sigma, successiveapproximation, Wilkinson, ramp-compare, delta encoded, pipeline,integrating, etc.

In some examples only a subset of the analog channels 50 are convertedat any given time; in other examples all of the analog channels 50 maybe converted. The plurality of digital signals output by the ADC circuitcan be assessed on one or plural digital signal processors (DSP) 70, ormay be analyzed together in single processor. For power saving purposes,and to take advantage of modular design, it may be suitable to usededicated DSP to yield a digital signal for use in detection circuits80. Any suitable DSP circuit can be used at 70.

One element of DSP may be the inclusion of a digital filtering circuitto narrow the band of signals to a range generally between about 10 and40 Hz, though wider or narrower ranges may be used. In addition, linesignal filtering at 50 or 60 Hz, depending on geography, may beimplemented in the DSP.

In some examples, a DSP has multiple stages. For example, a DSP may havefive filter stages with each stage being a configurable bi-quad filter,or other filter. One or more stages may be used for 50 and 60 Hz notchfilters to eliminate line noise. A bandpass can be generated with twoother stages by having a low pass filter in the range of 15-40 Hz, orabout 25 Hz in another example, and a high pass filter in the range of 1to 15 Hz, with 9 Hz serving as one example. Where multiple signals areprocessed in parallel, not all signals will necessarily be filtered thesame and, in some examples, one of the signals may filtered severaldifferent ways.

In some examples the individual detection blocks at 80 each use aseparate cardiac cycle detection method to identify heart beats for usein one or more of defining a cardiac cycle signal for morphology (shape)analysis, and or to count cardiac cycles per unit time to generate acardiac rate for a given chamber of the heart. Individual detectionblocks at 80 may each use the same method of cardiac cycle analysis, ordifferent methods may be selected for different digital signals. Forexample, if one detection line is configured for use on a signalcaptured using two intracardiac electrodes, and a different detectionline uses a signal captured using two subcutaneous electrodes, thedetection lines would likely each use a different mode of detection, asthe intracardiac signal will look quite different from the subcutaneoussignal. Some examples of cardiac cycle detection (also sometimesreferred to as R-wave or beat detection) are shown in U.S. Pat. Nos.8,565,878 and 5,709,215, the disclosures of which are incorporatedherein by reference. Several methods are known in which a time varyingthreshold compared against the received cardiac signal until thethreshold is crossed, at which point a beat or new cardiac cycle may bedeclared.

FIG. 3-5 show illustrative methods in block flow form. A firstillustration in FIG. 3 shows the combination of multiple vector sensingsignals from the very start of analysis. The illustrative method 100begins by combining signals, as indicated at 110, to convert three datastreams S1, S2, S3, indicated at 112, into a combined data stream Sc, asshown at 114.

This combined data stream is then filtered at 120, for example to abandpass in the range of 3 to 40 Hz, or more preferably about 9 to 25Hz, or other ranges as suited for a particular application. Filtering120 may be performed in association with amplification and may beperformed on either an analog signal or a digital signal, or both.Filtering may further include DC blocking filters and/or the applicationof a notch filter(s) to take out 50 and/or 60 Hz line noise. Weightingfactors may be applied to the analog domain signal for example by usingadjustable gain circuitry in the input prior to analog-to-digitalconversion. Weighting factors may be applied during analog-to-digitalconversion, or on the digital signal after analog-to-digital conversion.

The filtered combined signal goes to a detection stage at 122, whereindividual cardiac cycles or beats may be detected. For example, anamplitude or magnitude measure generated using the combined signal canbe compared to a detection threshold, wherein the detection thresholdmay be a time varying threshold. Upon crossing of the detectionthreshold, a new cardiac cycle may be declared. Individual detectedcycles, standing alone or in small groups, or as a series of events, maythen go through a certification stage 124. Certification 124 mayinclude, for example, analyzing one or more signals to determine whetherthere is noise in the signal, or analyzing detected events in pairs orsmall groups or as a series to determine whether any overdetected eventshave taken place. An overdetected event may occur if/when multiplecardiac cycles are declared but only one such cycle took place, or if acardiac cycle is declared without a new cardiac cycle having occurred.Upon removal of noise and overdetections, the certified cardiac cyclesare passed to a decision phase 126 which may use one or more of the rateat which cardiac cycles are detected and/or the morphology (shape) ofthe cardiac signals associated with cardiac cycles to determine whethera treatable or otherwise targeted cardiac state is occurring. Thedecision phase 126 may include updates to the heart rate 128.

Returning now to block 110, there are several enhancements available inseveral different illustrative examples. For example, assuming threesensing vectors (though more or fewer can be used), the combined datastream Sc can be calculated as using this formula:

S _(c) =k ₁ *S ₁ +k ₂ *S ₂ +k ₃ *S ₃  (Formula 1)

In this equation, each of the k-factors is a weighting factor. Theweighting factor may be determined by consideration of one or moresignal quality metrics. For example the weighting factor for the nthsensing vector may be generated as:

k _(n) =A _(n) *R _(n) *V _(n) *M _(n) *P _(n) *N _(n)

Where A is an amplitude measure for the desirable signal of the nthvector, such as the peak cardiac R-wave, the largest excursion frombaseline during a QRS complex, or the peak-to-peak measurement of theQRS complex. A larger amplitude measure, within boundaries for thedynamic range of the device hardware, generally would yield a highervalue for A. As an alternative, the factor A may be used to correct foramplitude variation for high quality vectors; for example, in the abovemath, the fact that one sensing vector signal has higher amplitude wouldalready weight that signal higher than a lower amplitude signal withoutseparate application of a weighting factor; therefor the A factor may beused to normalize amplitude for any sensing vector signal that is in adesired range above the noise floor and below the maximum dynamic rangefor a device. An alternative formulation may take the form of:

k _(n) =f(A _(n) ,R _(n) ,V _(n) ,M _(n) ,P _(n) ,N _(n))

Where the weighting factor, k, may be a function or set of functions ofthe various component using, for example, exponential or logarithmicvalues and/or look-up tables, or addition, subtraction and otheroperators.

The individual factors may vary widely. The factor R may be a ratio ofthe desirable signal to a noise measure, for example, the ratio of theR-wave to the next highest peak, T-wave, or average signal amplitude ormagnitude of the nth vector. A higher ratio of signal to noise may yielda higher value for R. V may be a measure of variability and/or stabilityfor a given vector, where variability may be determined in any ofseveral ways. For example:

-   -   the QRS width may be calculated for each of several cardiac        cycles, and variability of the width may be used;    -   R-wave peak height may be calculated and its variability        determined;    -   Signals for several cardiac cycles may be laid atop one another        and cross correlation, sample by sample variation, or other        measures of cycle to cycle variation may be determined;        Lower variability may be used to make for a larger value for V.        M may be a shape matching score, where shape matching indicates        that the detected cardiac cycles correlate to a stored template;        a higher match may yield a higher value for M.

P may serve as a correction factor to accommodate the polarity of thesignal in a given vector, where P is positive unity (+1) if the signalpolarity is positive, or negative unity (−1) if the signal polarity isnegative. For example, if cardiac R-waves are the desired signal andfocus for later detection steps, P would be used to ensure that thesummation to generate the combined signal does not cancel out thedesirable signal where one vector has R-wave peaks that are positive,and another vector has R-wave peaks that are negative. Alternatively,rather than including a polarity factor, the system may instead usemagnitudes or absolute values to prevent cancelling out.

P may indicate whether signal polarity suggests poor signal quality. Forexample, polarity may be identified for individual cardiac cycles byidentifying, for example, the largest peak, or the first in time peak ofthe QRS complex, or the peak having the greatest energy, and associatingwhichever polarity, positive or negative, the identified peak has as thepolarity of the signal for a given cardiac cycle. In some embodiments,polarity may be used to select a fiducial point for template alignmentor a template for comparison; variation in polarity can make templateanalysis unreliable. If identified polarity changes from beat to beat oracross a set of detections, this may be used to identify poor signalquality.

A noise factor, N, may be included as well. The noise factor may bedetermined by, for example, determining the average, mean, or RMS valueover a block of time (i.e. one second) for a given sensing vector, orfor a portion thereof after excluding a desirable signal such as thecardiac R-wave or P-wave either by subtraction or by windowing out apart of the time interval. Higher average, mean, or RMS values arelikely related to noisier vectors. The number of turning points orinflection points in the signal may be counted, as higher numbers ofturning points or inflection points can suggest a noisier sensingvector. More noise may equate to lower quality and hence a lower valuefor N.

A further example may include a factor to account for the likelihood ofoverdetection occurring on a given vector, either projected by analysisand/or based on history of a given sensing vector; such a factor couldbe, for example, one minus the percentage of detected beats in aprevious day, hour or other period of time, which have been marked asdouble detection for a given sensing vector. Since the certificationstage 124 where overdetection or noise detections are flagged isperformed in method 100 on the combined signal (after filtering 120 anddetection 122), the method may take advantage of parallel processingcapabilities to process a combined signal for purposes of analyzingcardiac rhythm on one data stream or channel, and processing a selectedindividual sensing vector signal for purposes of updating the weightingfactor k for a given vector, including such steps as identifying any ofthe above subcomponents of the weighting factor as well as applyingcertification assessments to identify noise or overdetection.

The mathematical functions of addition and/or multiplication may beswapped with each other or with other methods. Fewer, more, or differentfactors may be provided as components of the weighting vector. In oneexample, each of the components is scaled to within boundaries of 0 to1, except for the polarity value P that, as noted, may be +1 or −1 in anexample. Scaling need not be applied. If desired, one or more of thevectors can be excluded from analysis by reducing the k-factor to zerofor the data stream generated from the excluded vector.

In an example, a physician or other user input may also be used tomodify the weighting factors k1, k2, or k3, if, for illustration, thephysician determines that one sensing vector is unsuitable for use. Inanother example, a secondary process such as a lead monitoring functionmay be used to modify or zero out one of the weighting factors if, forillustration, a lead or electrode is determined to be floating (that is,its position is poorly controlled), damaged, or fractured, for example.

In another example, an attempt at forming a template of an ongoingcardiac rhythm may occur, in which template formation calls for a matchof a given cardiac cycle signal to one or plural adjacent cycle signals;failure of template formation would indicate a varying signal and may beused to determine that a given sense vector is of lower signal quality.In several examples, one or more of the weighting factors k1, k2, k3and/or the components thereof are recalculated in one or somecombination of the following:

-   -   All or some components are recalculated with each new detected        cardiac cycle;    -   All or some components are recalculated at regular intervals        (i.e. time blocks of 1 to 60 seconds, for example, or more or        less);    -   All or some components are recalculated in response to a        triggering event, where a triggering event is one or more of:        -   Determination that a patient has changed postures;        -   Detection of a change of intrinsic cardiac rate;        -   Identification of one or more noisy or overdetected cardiac            cycles;        -   Determination that the detected heart rate has exceeded a            threshold or fallen below a threshold;        -   Determination that signal quality of one or more sensing            vectors has changed by periodic or continuous review of            signal quality for one or more such vectors;        -   Determination that signal quality represented in the            combined signal Sc has changed;        -   In a device that uses one or more of an X-out-of-Y counter            or number of intervals to detect (NID) analysis to determine            whether a treatable arrhythmia is taking place, the meeting            of a therapy or other threshold by the X-out-of-Y counter or            NID analysis;        -   Divergence between cardiac rate as calculated using the            combined signal Sc and a cardiac rate calculated by some            other device or method, where, for example, the other device            may be a separate cardiac device, a blood pressure sensor,            or a pulse oximeter, and/or the other method may be an            autocorrelation or other non-cardiac-cycle based measurement            of cardiac rate;    -   Recalculation may also be triggered in response to physician        and/or patient input in some examples as provided for example        via a patient remote control, an in-home monitoring device for        an implantable or wearable device, or a physician/clinical        programmer.        Autocorrelation is noted in the above list and may take the form        as shown in copending U.S. patent application Ser. Nos.        14/819,817, 14/819,851, and 14/819,889, the disclosures of which        are incorporated herein by reference. Autocorrelation may also        be performed using other methods.

FIG. 4 shows another example. Here, a filtering step 150 is performedfirst on a set of signals 152, which are then passed at 154 to acombining step 156. The combined filtered signal 158 (as opposed to thefiltered combined signal 114 in FIG. 3) passes to detection 160,certification 162, decision stage 164, and updating the heart rate 166.The difference relative to FIG. 3 is that the signal combination takesplace after filtering has been performed.

FIG. 5 shows another example method 200. This example includes anevaluation of sensing vector signal quality at 210, creation of weightedsum signal at 212, analysis of the cardiac signal at 220, and adetermination of whether there is a need to re-evaluate signal qualityat 240. Step 240 may consider any of the triggers noted above forrecalculation of vector weights using vector signal quality. If there isno need to recalculate signal quality at block 240, the method loops to212 where a new weighted sum signal is calculated.

Within block 220, the method waits for a detection 222 of a new cardiaccycle. Noise is evaluated on each of the sensing vector channels 224,which may encompass all or a subset of the individual sensing vectors. Adetermination is made at 226 whether there is noise on all of thesensing vector channels 224. If so, the new detection from block 222 ismarked as noise as indicated at 228 and the method returns to block 222to await a next detected cardiac cycle.

If block 226 yields a no result, the method determines at 230 whetherthere is noise on any channel; if so, the weight applied to one or moresignals at step 212 may be adjusted as indicated at 232, including, forexample, setting the weight to 0 for sensing vectors that are noisyeither one time or persistently. Next, the certification phase isapplied at 234 (after either of block 230 or 232) to eliminateoverdetection or noise on the combined signal itself. The process thengoes to the decision phase 236 and may include updating the calculatedheart rate, if desired.

An outcome, or quantity of outcomes, finding noise in one or both ofblocks 226 and/or 230 may be used to trigger a decision to re-evaluatesignal quality in block 240 in some examples.

In an alternative embodiment, the combined signal may use a vector mathapproach in place of simple summation shown in Formula 1, above. Forexample, a plurality of sensing vectors may be combined in the followingmanner to yield a “conversion” to a spherical set of coordinate values:

$r = \sqrt{( {k_{1}*S_{1}} )^{2} + ( {k_{2}*S_{2}} )^{2} + ( {k_{3}*S_{3}} )^{2}}$$\theta = {\cos^{- 1}( \frac{k_{1}*S_{1}}{r} )}$$\phi = {\tan^{- 1}( \frac{k_{2}*S_{2}}{k_{3}*S_{3}} )}$

This basic approach presumes that the three sensing vectors areorthogonal, without correction. This simplification may be sufficient insome contexts. However, it may be useful for some embodiments to includecorrection factors for each of the k weights to account fornon-orthogonal configuration of sensing vectors

FIG. 6 provides an example for the generation of corrective inputs. Forexample, fiducial points may be applied to a patient to provide a frameof reference. For example, the patient may be asked to assume a posture(sitting, standing, lying down, etc.), and fiducials may be applied tothe patients skin and or provided in one or more implantable positionsin the heart, for example, or by use of a fluoroscopic agent to allowimaging of the heart. The application of fiducials at 300 is followed byobtaining an image at 302, for example by X-ray, and calculating atransformation 304 of the actual physical positions of the electrodes ofan implant to the position of the heart of a patient. This way, anactual cardiac vectorcardiogram can be generated relative to thepositioning of the physical features of the heart. The method may berepeated for a plurality of postures in order to allow specificcorrection for several patient postures, as the relative position ofelectrodes and the heart, or the electrodes to one another, may changeas the patient changes postures.

In a simpler approach, the fiducials 300 are omitted, and the relativeplacement of electrodes that define sensing vectors may be obtained.Again the assessment may be used to establish correction for variouspostures.

The outputs of an assessment as in FIG. 6 may be used to establish newweighting factors for each sensing vector to correct for non-orthogonaldisposition of the electrodes relative to one another and/or relative tothe patient/cardiac frame of reference. In another example, one orplural matrices are stored to provide correction factors by matrixmultiplication as follows:

$\begin{bmatrix}{k_{1}*S_{1}} \\{k_{2}*S_{2}} \\{k_{3}*S_{3}}\end{bmatrix} = {\begin{bmatrix}a & b & c \\d & e & f \\g & h & i\end{bmatrix} = \begin{bmatrix}P_{1} \\P_{2} \\P_{3}\end{bmatrix}}$

The correction factor matrix may be selectable based on the patient'sposture if desired.

From the combination of these vectors, the radius, r, can be used indetection blocks 122 (FIG. 3, after filtering at 120) or 160 (FIG. 4).The angular components may be used in detection if desired, but may alsobe used in diagnostic or pathological analysis.

In another example, rather than conversion to spherical coordinates, aconversion to cylindrical coordinates may be performed. Once in acylindrical coordinate system, the three variables would be (ρ, φ, z).The conversion, much like a conversion to spherical coordinates, cantake place with or without correction factors that accommodate positionof electrodes relative to one another and/or the patient's heart. Insome embodiments, the angular component can be ignored (or reserved forpathology analysis), leaving p and z, which may be handled using any ofthe methods shown herein for handling of a weighted sensing vectorsignal, for example, by combining the signal components prior tofiltering or cardiac cycle detection, and/or by combining results fromone or more of cardiac cycle detection, certification, and/or decisionstage analyses.

FIG. 7 shows another example in block flow form. In this method 350,filtering 352 occurs on multiple sense vector signals 354. The filteredsignals 356 are independently passed to a detection block 360 in whichcardiac cycles are detected on each of the incoming signals 356. Theoutput set of detected cardiac cycles on each signal 362 is thencombined, as indicated at 364. FIGS. 12 and 14 show pictorialillustrations of how the set of detections can be combined together. Inan example, where the cardiac cycle detections match, this can be viewedas likely affirming detection accuracy, and if mismatches occur, thismay suggest overdetection, noise, or other difficulty with sensing.

In some examples, spatial differences among the sensing vectors thatyield the incoming signals 354 may cause differences in the time atwhich cardiac cycle detection occurs in each vector. To account for suchdifferences, delays may be integrated where, for example, detection 360of a cardiac cycle may occur consistently at different times indifference data streams. Such delays may be referred to as phasecorrection or phase delaying one or more vectors signals and/or datafrom one or more signals.

Once the cardiac cycle results are combined at 364, the combined datastream 366 is passed on to certification 370 to check for in-signal, asopposed to cross-channel, indications of noise or overdetection. Thedecision phase 372 and heart rate update 374 follow in thisillustration.

FIG. 8 shows another example in block flow form. In the method 400filtering 402 is applied to multiple sense vector signals 404. Thefiltered signals 406 pass to detection 408, yielding data streams ofcardiac cycle detections 410. The detections 410 are passed tocertification 412 to check for noise or overdetection on the individualchannels, with outputs 414 then combined at 420. Examples may be seen inFIGS. 13 and/or 14 of the combining step at 420. In an example, mismatchof detection 408 and/or certification 412 can be used to mark events assuspect, noise, overdetection or true detections, for example. Thecombined results 422 are passed to the decision phase 424 and heart rateupdates 426.

FIG. 9 shows another example in block flow form. In the method 450,filtering 452 is applied to multiple sense vector signals 454. Thefiltered signals 456 pass to detection 458, yielding data streams ofcardiac cycle detections 460 that pass to certification 462 where noiseand overdetection can be screened out. Certified cardiac cycledetections 464 pass to the decision phase 466, with decision outcomes468 then combined at 470, with updates to the heart rate 472. As notedpreviously, decision phase 466 may assess various elements of thedetected signal including the morphology of detected cardiac cycles,rate, variation of the signal from beat to beat, changes relative to atemplate or multiple templates, width, and overall amplitude to makedeterminations regarding the cardiac state of the patient.

FIG. 10 shows another example in block flow form. FIG. 10 extends theconcept of FIG. 9 an additional step. Here there are separate datastreams or channels for each of first, second and third sensing vectorsignals at 502, 504, 506. Each data stream may represent analysis on asingle sensing vector, on a combined signal (i.e., k1*s1+k2*s2) as inFIG. 3, or a combined and converted/corrected signal such as thespherical or cylindrical coordinate examples discussed above. In stillanother example, two or more separate data streams may derive from onesource by, for example, subjecting the signal or combination of signalsto different weighting factors and/or filtering 510techniques/boundaries. Each data stream is separately analyzed throughfiltering 510, cardiac cycle detection 512, noise 514, overdetection516, and generation of a 4RR (or other average) beat rate 518.

Periodically, or at each detected event detection, or using some otherinput to drive analysis, a separate assessment is performed in method500 by comparing the rate results at block 520. If the rate results arein agreement, the overall heart rate can be updated at 524. If the rateresults do not agree at 520, then a further evaluation can be performedat 522. Several different techniques may be used at block 522:

-   -   In one example, the relative strengths or signal quality for        data passed into each of the separate data streams 502, 504, 506        may be compared to one another to determine whether one or more        is to be preferred or ignored    -   In another example, a separately sourced heart rate may be        referenced using, for example, pulse oximetry, heart sounds,        blood pressure measurements, or a rate derived from a second        wearable or implantable device, to determine which, if any, of        the rates that disagree at block 520 is correct or incorrect.    -   In another example, a heart rate derived from a        non-cardiac-cycle detection methodology, such as the        autocorrelation methods referenced above, is obtained to        determine which, if any, of the rates that disagree at block 520        is correct or incorrect.    -   In another example, it may be determined whether mismatch at 520        can be attributed to a chamber-specific cardiac condition, such        as a ventricular originating tachyarrhythmia, or a        non-conducted, or only partly conducted, atrial flutter or        fibrillation.    -   In another example, simple majority rule is relied upon at 520        if, for example, three data streams are used (as shown), and two        of the data streams agree, then the third data stream's        calculated rate may be excluded or ignored.    -   In another example, the detection 512 results from the several        data streams can be lined up relative to one another and cross        correlated (see FIGS. 12 and 14 below) to determine whether        patterns of overdetection may be occurring in more than one data        stream, and to see if aligned “true” detections can be extracted        to yield a corrected rate.    -   In yet another example, the mismatch of rate calculations can be        used to support a determination of a tachyarrhythmia, if several        data streams suggest a tachyarrhythmia, as illustrated for        example in FIG. 15, below.        Any of these techniques or combinations thereof may be used to        perform evaluation at block 522 to find a heart rate estimate at        524. Other techniques may be used in addition to or instead of        the above. For example, in one system, a tiered set of questions        is asked:    -   Do the rates from two of three (or other majority or plurality)        channels match; if so, then use the matched rate    -   Do the detections match upon assessment of individual detection        streams, either before or after eliminating one or more of noise        or overdetection; if so, then use the matched detection data to        generate a rate    -   Does one of the sense vectors show a higher sensing quality        metric (such as higher amplitude and/or higher signal to noise        ratio) than all others; if so, use the rate from that vector        These analyses may be used singly or in various combinations.

In another example, within block 522, a set of detections in separatedata streams may be assessed for the existence of a pattern orrandomness. If mismatch across several vectors occurs randomly, thelikely sources are either a noisy signal in one or more sensing vectorsor an actual arrhythmia detected on one or more sensing vectors. If, onthe other hand, mismatch is patterned, it is likely that malsensing istaking place due to overdetection. For random mismatch, the next stepcould be to rule out noise (by reviewing, for example, turning pointcounters for the sensing vectors 502/504/506 and comparing to thresholdsor to one another; a vector with far more turning points than the othervectors could be found to be noisy). If noise is ruled out, the fastestrate detected by any of the available sense vectors may be assessed todetermine whether a treatable condition is occurring.

Other tiered analyses may be used in other embodiments by combining oneor more of the techniques noted for block 522.

FIG. 11 shows another example in block flow form. Here, resultscombination occurs repeatedly throughout the process while individualsensing vector analysis continues in parallel. In the illustrativemethod 550, filtering 552 is applied to multiple sense vector signals554. The filtered signals 556 pass to detection 560, which provides aset of detection outputs 562. In addition, the outputs of the detection560 may be combined at 564 in a manner similar to that of block 364 inFIG. 7.

The combined cardiac cycle detection output 566 is passed tocertification 570 along with the individual detection outputs 562.Certification 570 again addresses noise and/or double detection to yieldoutput data streams 572 that may include, for example, a data stream foreach of the individual detection outputs 562 as well as a data streamfor the combined detection results 566. In addition, again, a separatecombining block is shown at 574 where the several individual andcombination outputs from certification 570 may be combined together in amanner similar to block 420 in FIG. 8.

The now up to five (or more or less) data streams are provided to thedecision phase at 580. Here, the method 550 is allowed to considerduring the decision phase 580 the individual certified detectionoutcomes, plus the certified combined detection outcomes, plus thecombined certified outcomes. The decision phase 580 may not only assessthe cardiac state, but may also identify signal quality metrics bycomparing the various results provided to it. The outputs 582 of thedecision phase 580 for each individual and combined input can then becombined together at 584 and used to determine not only cardiac statebut also to generate an updated rate at 590.

FIG. 12 includes representations of cardiac electrical signals along twosensing vectors and corresponding cardiac cycle detections todemonstrate an illustrative method. The graph 600 shows a first cardiacsignal 610 and corresponding cardiac cycle detections 612, and a secondcardiac signal 620 with corresponding cardiac cycle detections 622. Inthis example, the detection outputs 612 and 622 can be compared to oneanother to identify an overdetection at 616. This is because, while thesingle detections at 614/624, and later at 618/628 temporally line upwith one another, at 616 there are two detections while at 626 there isa single detection. There are several rule sets which can be applied todetermine that at least one detection at 616 is an overdetection:

-   -   In one example, there must be aligned cardiac cycle detections        both before and after the overdetection; here these could be        detections 614/624 and 618/628, or, alternatively, one could use        the first of the two detections at 616 with detection 626, and        subsequent detections 618/628    -   In one example, there would have to be two closely spaced        detections, such as those at 616, with an interval between them        of less than a preset threshold or less than approximately half        the prevailing interval on either the sensing vector on which an        overdetection is found or on a second sensing vector.    -   In one example a set of two consecutive intervals on one sensing        vector/channel have to add up to either a preceding or following        interval on that vector. Here, the interval between detections        616, when added to the interval between the latter of detections        616 and detection 618, is the same as the preceding interval        between detection 614 and the first of the two detections at        616.    -   In one example, a set of two consecutive intervals on one        sensing vector/channel have to add up to an interval on a second        sensing vector. Here, the interval between detections 616, when        added to the interval between the latter of detections 616 and        detection 618, is the same as the interval from detection 626 to        detection 628.        These rules may be used singly or in various combinations. Other        rules may apply in addition to or instead of any of these.

FIGS. 13-15 show cardiac cycle detections in two channels forillustrative methods. FIG. 13 shows cardiac cycle detections, as treatedby a certification stage, for a first channel 640 and second channel642. At 650, a detection takes place in each channel, however, thedetection in the second channel 642 is marked as noise (indicated by the“N” marker). This creates a conflict between the two channels 640/642,which can then be resolved in one of several ways:

-   -   In one example, the detection at 650 on the first channel is        reassessed for noise using a lower standard than previously        applied. For example, if a turning points analysis is used for        noise in which the number of turning points in a period of time        is compared to a threshold and, if the threshold is exceeded,        noise is declared, the threshold can be lowered to more readily        identify the event at 650 as noise. If the lowered threshold is        still passed, the noise flag at 650 may be treated as incorrect;        if the lowered threshold is not passed, the noise flag at 650 is        confirmed.    -   In another example, the spectral content of the sensed event at        650 on the first channel 640 is assessed for noise; if the        spectral content suggests noise, then noise is confirmed.    -   In another example, the intervals around the noise flag are        analyzed both with and without treating the detection at 650 in        each channel as noise. If treating the detection at 650 as noise        makes the intervals more consistent, then noise is confirmed; if        treating the detection at 650 as not noise makes intervals more        consistent, then noise is not confirmed.    -   In another example, it may be judged whether the two detections        at 650 are aligned similar to other detections in each channel;        if misaligned, then the noise in one channel may be confirmed        while noise in the other channel is not confirmed, suggesting        that the noise in one channel may have prevented a true        detection from occurring at a different point in time.    -   In one example, any noise marker on any channel causes treatment        of all detections on all channels within a window of time        associated with the noise marker as noise.    -   In another example, when a noise marker is identified, it is        next determined whether any of the electrodes used to sense the        signal in which the noise marker is placed are being reused by        other sensing vectors; if so, the other sensing vectors which        reuse one of the electrodes may have any close-in-time detected        cardiac cycles also marked as noise.        These rules may be used singly or in various combinations. Other        rules may be used in addition to or instead of these.

Also in FIG. 13, at 652, a double detection marker appears in the secondchannel, but not in the first channel. Here, the double detection markerwould be confirmed, as first channel fails to have a correspondingdetected cardiac cycle at time 652, but does have 1:1, aligned sensedevents around the double detection marker 652. As noted above, otherrules may be applied to confirm a certification determination.

FIG. 14 shows another example. Here a string of what may be any ofcertification outcomes, cardiac cycle detection outcomes, or decisionphase outcomes are shown for a first channel 670 and a second channel672. It can be seen that for the detections on the first channel 670,there are corresponding detections on the second channel on a 1:1 andaligned in time (at least as shown) basis. It should be noted that insome examples, the alignment such as shown at 680 and 688 may be basedon the use of an offset applied to data from the first or secondchannels 670, 672, as detections may occur at consistently offset timesin multiple sensing vectors.

For the detections at 682, 684 and 686, which occur only on the secondchannel 672, the combinational analysis of both sensing vectors revealsoverdetection. In one example, a single overdetection event such as at682 may be identified standing alone. In other examples, multiplepotential overdetections in proximity, such as at 682, 684, may be usedto confirm suspected overdetection. In still further examples,additional data may be sought to confirm overdetection at 682, 684, 686by various methods:

-   -   In an example, morphology analysis is performed to observe        divergence of the detections in the second channel at one or        more of 682, 684, 686 from other detections. Divergence may be        identified by, for example, looking for differences in overall        amplitude, signal width, spectral content, shape (by correlation        analysis, principal component analysis, or other review).    -   In an example, a third data source may be brought to bear, such        as a combination of the first and second channels, or review of        heart sounds or pulse oximetry data.    -   The potential overdetections at 682, 684, 686 may be passed        through overdetection analysis (such as, for example, in U.S.        Pat. Nos. 8,160,686 and 8,160,687, for example) with modified        rules that make it easier to identify overdetection such as, for        example, if an alternating morphology analysis is used, by using        modified thresholds for determining whether a match or no match        exists, or by lowering standards used to identify alternating        intervals.        These analysis may be used singly or in various combinations.        Other analyses may be used in addition to or instead of the        above.

FIG. 15 shows an example in which post-decision data streams may becombined (though other steps in the method may be similarly assessed).Here, the combination of data streams confirms a potential arrhythmiapattern. Data is shown for a first channel at 700 and a second channelat 702. At 710, a sensed event or cardiac cycle is observed in alignedfashion on each channel. Following a long pause 712 (which can be amarker of arrhythmia onset), additional sensed events occur at 714, 716,718 across the two channels, but the sensed events may no longer bealigned (though they could be). Eventually, as shown at 720, theaccompanying rate exceeds a threshold such that the “S” markers, whichare used in this example for lower rate detected cardiac cycles, become“T” markers indicating a high rate. Misalignment across the two vectors,as well as high rate conditions in each vector, suggest arrhythmia.Moreover, the prior alignment, and long pause 712, are also indicatorsof tachyarrhythmia. If a noise or double detection marker were to arisein either channel, these factors identified the combination analysis maybe used to affirm continued arrhythmia or, alternatively, find a likelysensing problem and potentially delay therapy:

-   -   The existence of prior alignment and later misalignment suggests        a change in cardiac rhythm, supporting a finding of treatable        arrhythmia; conversely consistent and continued alignment may        suggest an organized rhythm which may or may not be misdetected.    -   The long pause on each sensing channel followed by the abrupt        change in signal characteristic suggests a sudden onset,        supporting a finding of treatable arrhythmia; conversely a        slower transition to higher rates may suggest an exercise        induced tachycardia not needing therapy    -   Lack of noise or double detection markers in each vector        suggests arrhythmia detections may be true; presence of one or        the other suggests higher scrutiny using additional data input        or analysis may be suitable

FIG. 16 illustrates a signal analysis method in which a signal isoverlaid with a filtered version of itself. For example, a signal fromone sensing vector, or a weighted sum of signals from plural sensingvectors, may run through a first data stream or channel subject to afirst set of filtering rules, and at the same time, run through a seconddata stream or channels subject to a second set of filtering rules. Theoutput may be combined, using reference to FIG. 11, after filtering 552and prior to detection 560, to provide an output for detection purposes.

The example of FIG. 16 goes a step further by switching which operationto perform during different time windows. In this example, the originalsignal is shown at 750, and the resulting signal is shown at 752. Duringfirst window 760, the original signal 750 as filtered with firstparameters, is subtracted from itself as filtered using secondparameters. During second window 762, the original signal 750 asfiltered with the first parameters, is added to itself as filtered usingsecond parameters. The resulting signal emphasizes the signal of thesecond window 762. The two windows, 760, 762 may be triggered byreference to the original signal 750 as filtered using the first orsecond parameters, or other parameters, or by reference to some othersignal. In one example, the second windows correspond to a time periodfollowing cardiac event detection on the signal 750. In this way, signalfor use in morphology analysis is generated at 752 by making adjustmentsin light of the signal 750 used for cardiac cycle detection.

FIG. 17 shows another example in block flow form. In FIG. 17, aplurality of inputs 770 are passed into a combination analysis 772 whichmay take the forms shown above and/or in FIGS. 18-20, below, leadingtoward calculation of a new heart rate estimate at 774. The inputs at770 are each weighted with a corresponding nth weighting factor. Inparallel to the combination analysis 772, one of the vectors is selectedas shown at 780 and is analyzed at 782 to update the weighting factorfor that vector. The selection of a sensing vector at 780 and updatingof the weighting factor may be a process that occurs continuously, withdifferent vector selections cycling as completion of updating of a givenweighting factor is completed. For example, the updating of weightingfactor at 782 may occur each minute for each sensing vector by cyclingthrough each of the vectors in the selection step 780 repeated. Otherintervals (every second, minute, hour or once daily) may be used. Ratherthan, or in addition to, interval based updating, a process of updatingin response to a triggering condition may also be used.

FIG. 18 shows another example in block flow form. Here the methodincludes calculating a set of weighting factors k1 . . . kn, at 800.Included in this analysis at 800 may be the calculation of phasedifferences among the vectors, as noted at 802, to allow for alignmentof detected cardiac cycles across vectors as in FIGS. 12-15, forexample. The calculated weighting factors are used at 810 to modify thesensing data streams, which are subject to signal analysis at 812. Atriggering event 814 can be used to exit the signal analysis block torecalculate the weight factors in block 800, again potentially includingphase calculation 802. The triggers may be period based 816 (timeintervals, for example), or may be based on detected events orconditions 818 such as various occasion-based triggers noted above.

FIG. 19 shows another example in block flow form. In this example, aplurality of signal sources, such as data (weighted or not) from severalsensing vectors are captured at 850. These signals are converted at 852into a separate coordinate system such as cylindrical coordinates tospherical coordinates. In this example, the scalar outputs (that is,omitting the angular outputs of the conversion) are obtained at 860 andpushed to analysis block 862 for cardiac event detection and the like,leading to calculation of a heart rate estimate. If more than threeseparate vectors are captured at 850, then other conversions may beperformed in block 852 to accommodate 4 or more dimensions of thecaptured signal. Alternatively, the multiple vectors may becross-correlated or averaged to pare down to a 3-dimensional spatialcoordinate for any given sample.

FIG. 20 shows another example in block flow form. Here, first and secondcardiac cycle detection data streams are obtained at 900, 902. It isthen determined whether for the two streams, prior alignment of data hasbeen observed, as noted at 904. Alignment may refer to the point in timewhere a detected cardiac cycle is declared, or relative to a fiducialpoint, such as a highest peak, or inflection point before or after ahighest peak. For example, alignment may be found if:

-   -   Detections, or fiducial points, in the first stream 900 occur at        the same time as detections, or fiducial points, in the second        stream 902, or within a predefined window (such as 10-50        milliseconds, or wider or narrower window); or    -   Detections, or fiducial points, in the first stream 900 occur at        a stable or predictable delay relative to detections, or        fiducial points, in the second stream 902; or    -   Detections, or fiducial points, in the second stream 902 occur        at a stable or predictable delay relative to detections, or        fiducial points, in the first stream 900.        If there is no alignment, then the method exits at 906, as        cross-vector assessment would not yield useful information. A        flag may be set at block 906 since one would generally expect        that in most systems there would be correlation in time between        cardiac cycle detections across vectors. However, with unusual        anatomy or cardiac conduction structures/behavior, it is not        implausible that a particular system/patient would fail to have        the sought-for alignment.

If prior alignment 904 is found, then the method proceeds to determinewhether there is a current alignment of cardiac cycle detections at 908.If so, then the detections may be confirmed at 910, subject toassessment for noise and/or overdetection using analysis of the signalsin each data stream.

If there is no alignment at 908, this may trigger, optionally, a secondassessment as noted at 912. Such second assessments are noted above andmay include re-assessment for noise or overdetection of misaligneddetected events using modified (reduced) thresholds, for example.Malsensing, if found, may be identified as noted at 914, either afterthe optional second assessment 912, or automatically from themisalignment found at 908.

The second assessment 912 may confirm the accuracy of detection forextra or misaligned detected events, and would lead to a differentoutcome than malsensing (not shown in FIG. 20). Such a finding may leadto a conclusion that there has been a change in sensing/detection orcardiac state, or may trigger a secondary analysis to determine whethersuch a change has taken place; for example, whether any of the currentsensing vectors continue to match a template from a known cardiac statemay be determined and, if no matches are found, new templates for a newcardiac state may be formed. The method or device may triggerreassessment, for example, of the various sensing vectors available tothe system, or the weights or phase delays associated with one or moresuch vectors, recording of data associated with the potential change ofsensing/detection or state, or setting of a flag, for example, to have aphysician review captured data.

In another example, malsensing 914 may be identified where previously“aligned” detections across two sense vectors are begin appearing in adifferent temporal alignment. For example, given vectors V1 and V2, ifcardiac cycle detections on V1 and V2 occur synchronously during a firsttime period, and then later occur with a 60 millisecond offset at alater time, it may be that one of the vectors is no longer triggeringcycle detections on the R-wave. For example, the P-wave could be causingcycle detections to occur in one vector, while the R-wave is detected inthe other vector; since the P-wave occurs prior to the R-wave, thiscould lead to an offset. The “Second Assessment” at 912 may include, forexample, a peak searching step to determine whether the true amplitudepeak for each cardiac cycle in each vector is occurring at an expectedtime relative to cycle detections, in order to determine which vector isexperiencing unexpected detection timing.

The blocks shown in FIGS. 17-20 may each be implemented as means toperform various analysis steps in several ways. For example, a means tocalculate a new weighting factor for a given sensing vector may take theform of a block of software code for implementation/execution by aprocessor, controller, microprocessor or microcontroller. A means tocalculate a new weighting factor for a given sensing vector may includeor consist of dedicated hardware or an analog, digital or mixed signalapplication specific integrated circuit (ASIC). Likewise, other blockson FIGS. 17-20 may be implemented as software and/or hardware.

FIG. 21 shows an implantable monitor. An implantable monitor may beimplanted subcutaneously in most instances, though other positions suchas intracardiac, epicardial, or below the ribs or behind/beneath thesternum may be used instead. The monitor 1100 is shown as having a firstsensing electrode 1102 on a header 1104 that may also include, forexample, an antenna for communicating with an external or secondinternal device. A second sensing electrode is shown at 1106 on theopposite end of the device 1100 from the first electrode 1102. Thesecond sensing electrode may be provided on the outside of a battery1108, for example, which may or may not be rechargeable. Operationalcircuitry for this design may be provided in the central portion of thedevice, as indicated at 1110. A third sensing electrode 1112 is shown inphantom to indicate that it may be on the opposite side of the devicefrom the first and second electrodes 1102, 1106. Other dispositions ofthe multiple electrodes may be used instead, such as those shown in U.S.Pat. No. 5,331,966, or those used in commercially available implantablecardiac monitors such as the various Medtronic Reveal™ products.

FIG. 22 illustrates a wearable cardiac rhythm management device. Thesystem is shown on the torso 1150 of a patient relative to the heart1152 of the patient. The external device may include, for example, acanister 1160 having a power source and operational circuitry for thedevice, as well as a plurality of leads 1162, 1164, 1166 connected tocutaneous electrodes on the front or back of the patient's torso 1150.It is understood that the system may provide therapy or may be merely amonitor, and may take other forms. The system may be, for example,integrated in a wearable vest, or provided as an automated externaldefibrillator, or may be a smaller wearable product such as a Holtermonitor or wearable patch, for example.

For the purposes of the present invention, the implantable therapysystem (FIG. 1), implantable monitor (FIG. 21), or external device fortherapy or monitoring (FIG. 22) may integrate the various improvementsshown herein so long as there are multiple sensing configurationsavailable. While most of the above discussion focuses on theavailability of multiple sensing vectors, a sensing reconfiguration mayinstead call for changing one or more of sensing gain, sensingfiltering, data rate, sampling rate, or other sensing features, inaddition to or instead of simply considering a different sensing vector.

Various examples above may be implemented in wearable or implantabledevices such as the devices shown in FIGS. 1, 21 and 22. Suchimplementation may take place by including operational circuitry forreceiving a signal from implantable electrodes, processing the signaland analyzing the processed signal to make decisions such as whether tostore data or deliver therapy. Operational circuitry may be housed in acanister or canisters. The operational circuitry may include acontroller (such as a microcontroller or microprocessor, or simply anapplication specific integrated chip (ASIC) such as an analog, mixedsignal, or digital ASIC).

The operational circuitry may instead or also include suitable analogand/or digital circuits needed for signal processing, memory storage andgeneration of high-power electrical, low-power electrical and/ornon-electrical outputs. The operational circuitry may include suitablebattery technology for an implantable device (rechargeable or primarycell), with any of numerous examples well known in the art, and may usevarious capacitor technologies to assist in the short term build-upand/or storage of energy for defibrillation or other output purposes.

The implantable or wearable components may be manufactured withbiocompatible materials suitable for implantation or tissue contact,such as those widely known, along with coatings for such materials,throughout the art. For example, implantable devices can be made usingtitanium, with a titanium nitride or iridium oxide (or other material)coating if desired, and implantable leads can be formed with abiocompatible material such as a polyether, polyester, polyamide,polyurethane, polycarbonate, silicon rubber and blends or copolymersthereof. Alternatively, other biocompatible materials such as silver,gold, titanium, or stainless steel such as MP35N stainless steel alloy,or other materials may be used.

In some examples, the system may include one or more sensors to detectsignals in addition to the cardiac electrical signal that can becaptured using selected combinations of implantable or wearableelectrodes. Such additional sensors may include, for example,temperature sensors, accelerometers, microphones, optical sensors andchemical sensors, among others. The programmer 22 and implantable device12 may communicate with one another using, for example and withoutlimitation, inductive or RF telemetry, or any other suitablecommunication solution. The present invention may be embodied in asystem having any such characteristics.

A first non-limiting example takes the form of a cardiac rhythmmanagement device having operational circuitry for analyzing cardiacsignals using a least first and second cardiac sensing vectors and firstand second sensing channels, wherein the operational circuitry isconfigured to combine the first and second cardiac signals, theoperational circuitry comprising the following: a first calculator meansfor calculating at least first and second weighting factors for the atleast first and second sensing vectors (such as circuitry and orprogramming instructions represented in FIG. 5, block 220, for example);a first means for applying the first weighting factor to modify signalssensed with the first sensing vector (such as circuitry and orprogramming instructions represented in FIG. 3, block 110, FIG. 4, block156, or FIG. 5, block 212, for example); a second means for applying thesecond weighting factor to modify signals sensed with the second sensingvector (such as circuitry and or programming instructions represented inFIG. 3, block 110, FIG. 4, block 156, or FIG. 5, block 212, forexample); a first means for combining the signals from the first andsecond sensing vectors, as modified by the weighting factors, togetherfor analysis to detect cardiac cycles (such as circuitry and orprogramming instructions represented in FIG. 3, block 110 or FIG. 4,block 156, for example); and recalculation means for causing thecalculator means to recalculate the weighting factors on a triggered orcontinuous basis (such as circuitry and or programming instructionsrepresented in FIG. 5, block 220, for example).

A second non-limiting example takes the form of a cardiac rhythmmanagement device as in the first non-limiting example, wherein theoperational circuitry is includes a phase calculator (such as circuitryand or programming instructions represented in FIG. 7, block 360, forexample) for calculating a phase factor to apply to delay one of thefirst or second cardiac signal vectors for the combining step.

A third non-limiting example takes the form of a cardiac rhythmmanagement device as in any of the first two non-limiting exampleswherein the operational circuitry includes a third means for applyingfiltering to the first and second sensing vectors prior to applying theweighting factors (such as circuitry and or programming instructionsrepresented in FIG. 4, block 150, for example).

A fourth non-limiting example takes the form of a cardiac rhythmmanagement device as in any of the first two non-limiting exampleswherein the operational circuitry includes a third means for applyingfiltering to the first and second signals as modified by the weightingfactors (such as circuitry and or programming instructions representedin FIG. 3, block 120, for example).

A fifth non-limiting example takes the form of a cardiac rhythmmanagement device as in any of the first three non-limiting examplesfurther comprising: a second means for combining the signals from thefirst and second sensing vectors together, as multiplied by theweighting factors to yield a combined signal (such as circuitry and orprogramming instructions represented in FIG. 3, block 110 or FIG. 4,block 156, for example); and sampler means for sampling the combinedsignal for use in cardiac cycle detection (such as circuitry and orprogramming instructions represented in FIG. 5, block 240, for example).

A sixth non-limiting example takes the form of a cardiac rhythmmanagement device as in any of the first five non-limiting exampleswherein the operational circuitry includes means for performing parallelprocessing of at least first and second sampled and conditioned datastreams, wherein the first data stream comes from one of the at leastfirst and second sensing vectors, as modified by the weighting factors,and the second data stream comes from a combined signal of the first andsecond sensing vectors (such as circuitry and or programminginstructions represented in FIG. 3, block 124, for example).

A seventh non-limiting example takes the form of a cardiac rhythmmanagement device as in the sixth non-limiting example whereinoperational circuitry includes means for switching the first data streambetween the first and second sensing vectors, wherein the operationalcircuitry further includes a first means for analyzing the first datastream to update one or more of the weighting factors over time (such ascircuitry and or programming instructions represented in FIG. 5, blocks210, 220, for example).

An eighth non-limiting example takes the form of a cardiac rhythmmanagement device as in the seventh non-limiting example wherein theoperational circuitry further comprises: means for periodicallyswitching from the first sensing vector to the second sensing vector foranalysis in the second data stream at predefined intervals (such ascircuitry and or programming instructions represented in FIG. 10, blocks520, 522, for example); and means for occasionally switching from thefirst sensing vector to the second sensing vector for analysis in thesecond data stream in response to a triggering event (such as circuitryand or programming instructions represented in FIG. 10, blocks 520, 522,for example).

A ninth non-limiting example takes the form of a cardiac rhythmmanagement device as in any of the sixth through eighth non-limitingexamples wherein the operational circuitry includes a second means foranalyzing the first and second data streams for noise and if noise isfound in the first data stream but not in the second data stream, meansfor modifying a corresponding weighting value for whichever of the sensevectors is in the first data stream at the time of the noise tounderweight that data stream (such as circuitry and or programminginstructions represented in FIG. 5, blocks 224, 226, 230, 232, 234, forexample).

A tenth non-limiting example takes the form of a cardiac rhythmmanagement device as in the ninth non-limiting example wherein theoperational circuitry is configured such that if noise is found in thesecond data stream, one or more detected cardiac cycles is discarded(such as circuitry and or programming instructions represented in FIG.5, blocks 224, 226, 230, 232, 234, for example).

An eleventh non-limiting example takes the form of a cardiac rhythmmanagement device as in any of the first ten non-limiting exampleswherein the operational circuitry is configured such that: the weightingfactors are comprised of an ordered series of individual weightingmultipliers having at least first and second values (such as circuitryand or programming instructions represented in FIG. 5, blocks 224, 226,230, 232, 234, for example); the step of applying the weighting factorsis performed by determining that a new cardiac cycle has been detected,and then beginning with a first of the ordered series of individualweighting multipliers, multiplying the weighting multipliers byindividual signal samples from the sensing vector (such as circuitry andor programming instructions represented in FIG. 5, blocks 224, 226, 230,232, 234, for example); and the weighting factors vary in weight fromone another by having those which are applied first in time be of lessweight than those applied later in time (such as circuitry and orprogramming instructions represented in FIG. 5, blocks 224, 226, 230,232, 234, for example).

A twelfth non-limiting example takes the form of a cardiac rhythmmanagement device having operational circuitry for analyzing cardiacsignals including a least first and second cardiac sensing vectors andfirst and second sensing channels, wherein the operational circuitry isconfigured to combine the first and second cardiac signals, theoperational circuitry comprising the following: converter means forconverting data from the at least first and second cardiac sensingvectors into one of spherical and cylindrical coordinates (such ascircuitry and or programming instructions represented in FIG. 19, block852, for example); generator means for generating a scalar output fromthe at least one of spherical and cylindrical coordinates (such ascircuitry and or programming instructions represented in FIG. 19, block860, for example); means for performing analysis to detect cardiaccycles using the scalar output (such as circuitry and or programminginstructions represented in FIG. 19, block 856, for example); and meansfor retaining one or more components of the special or cylindricalcoordinates to use in addition to the scalar output for identifyingoverdetection resulting in the step of performing analysis to detectcardiac cycles using the scalar output (such as circuitry and orprogramming instructions represented in FIG. 19, block 860, forexample).

A thirteenth non-limiting example takes the form of a cardiac rhythmmanagement device as in the twelfth non-limiting example wherein theoperational circuitry includes means for applying a transformation to aset of data received using the at least first and second cardiac sensingvectors, wherein the transformation is generated by obtaining anormalized data transform to a frame of reference for a patientreceiving the implantable cardiac rhythm management device (such ascircuitry and or programming instructions represented in FIG. 6, block304, for example).

A fourteenth non-limiting example takes the form of a cardiac rhythmmanagement device as in the twelfth non-limiting example wherein theoperational circuitry includes means for acting upon the components ofthe converted spherical or cylindrical coordinates by applying a firstfiltering ruleset to a first data stream, and by applying a secondfiltering ruleset to a second data stream, and combining results of thefiltering of each of the first and second data streams (such ascircuitry and or programming instructions represented in FIG. 16, blocks760, 762, for example).

A fifteenth non-limiting example takes the form of a cardiac rhythmmanagement device having a least first and second sensing vectors andoperational circuitry for analyzing cardiac signals on at least threedata streams as follows: a first data stream for a signal on the firstsensing vector; a second data stream for a signal on the second sensingvector; and a third data stream for a signal calculated as a combinedsignal generated by combining signals from at least the first and secondsensing vectors; wherein the operational circuitry comprises thefollowing: identifier means for identifying a potential new cardiaccycle by analysis of at least the third data stream (such as circuitryand or programming instructions represented in FIG. 5, block 222, forexample); means for determining whether there is noise on any of thefirst, second and third data streams (such as circuitry and orprogramming instructions represented in FIG. 5, block 224, for example)and, if so, do one of the following: if noise is present on all threedata streams, discard data associated with the potential new cardiaccycle (such as circuitry and/or programming instructions represented byblocks 226 and 228 in FIG. 5); or if noise is present on less than allthree data streams, change the manner in which the first and second datastreams are combined together (such as circuitry and/or programminginstructions represented by blocks 230 and 232 of FIG. 5).

A sixteenth non-limiting example takes the form of a cardiac rhythmmanagement device as in the fifteenth non-limiting example wherein theoperational circuitry includes combiner means for combining the signalsfrom the at least first and second sensing vectors by applying a firstweighting factor to the signal from the first sensing vector, andapplying a second weighting factor the signals from the second sensingvector (such as circuitry and or programming instructions represented inFIG. 5, block 212, for example); and the operational circuitry includesmeans for changing the manner in which the first and second data streamsare combined together if noise is present on less than all three datastreams by modifying one or more of the weighting factors (such ascircuitry and or programming instructions represented in FIG. 5, block232, for example).

A seventeenth non-limiting example takes the form of a cardiac rhythmmanagement device having a least first and second sensing vectors andoperational circuitry for analyzing cardiac signals on at least threedata streams as follows: a first data stream for a signal on the firstsensing vector; a second data stream for a signal on the second sensingvector; and a third data stream for a signal calculated as a combinedsignal generated by combining the first and second sensing vectors;wherein the operational circuitry comprises following: a first analyzermeans for analyzing the first data stream by filtering the data stream,and a first detector for detecting one or more cardiac cycles in thedata stream (such as circuitry and or programming instructionsrepresented in FIG. 10, blocks 510, 512, for example); a second analyzermeans for analyzing the second data stream by filtering the data stream,and a second detector for detecting one or more cardiac cycles in thedata stream (such as circuitry and or programming instructionsrepresented in FIG. 10, blocks 510, 512, for example); a third analyzermeans for analyzing the third data stream by filtering the data stream,and a third detector means for detecting one or more cardiac cycles inthe data stream (such as circuitry and or programming instructionsrepresented in FIG. 10, blocks 510, 512, for example); and means forcomparing the times at which cardiac cycles are detected in each of thefirst, second, and third data streams to determine whether any detectedcardiac cycles are likely incorrectly detected (such as circuitry and orprogramming instructions represented in FIG. 10, block 520, forexample).

An eighteenth non-limiting example takes the form of a cardiac rhythmmanagement device as in the seventeenth non-limiting example wherein theoperational circuitry is configured such that, before comparing thetimes at which the cardiac cycles are detected in each of the first,second, and third data streams, the operational circuitry first analyzesdetected cardiac cycles in the first, second, and third data streams, toeliminate noise-induced detected cardiac cycles.

A nineteenth non-limiting example takes the form of a cardiac rhythmmanagement device as in the seventeenth or eighteenth non-limitingexamples wherein the operational circuitry is configured such that,before comparing the times at which the cardiac cycles are detected ineach of the first, second, and third data streams, the operationalcircuitry first analyzes detected cardiac cycles in the first, second,and third data streams, to eliminate overdetected cardiac cycles.

A twentieth non-limiting example takes the form of a cardiac rhythmmanagement device having a least first and second sensing vectors andoperational circuitry for analyzing cardiac signals on at least threedata streams as follows: a first data stream for a signal on the firstsensing vector; a second data stream for a signal on the second sensingvector; and a third data stream for a signal calculated as a combinedsignal generated by combining the first and second sensing vectors;wherein the operational circuitry comprises the following: a firstanalyzer means for analyzing the first data stream by filtering the datastream, detecting one or more cardiac cycles in the data stream, andcertifying the detected cardiac cycles by removing noise and/oroverdetection (such as circuitry and or programming instructionsrepresented in FIG. 11, blocks 552, 560, 570, for example); a secondanalyzer means for analyzing the second data stream by filtering thedata stream, detecting one or more cardiac cycles in the data stream,and certifying the detected cardiac cycles by removing noise and/oroverdetection (such as circuitry and or programming instructionsrepresented in FIG. 11, blocks 552, 560, 570, for example); and a thirdanalyzer means for analyzing the third data stream by filtering the datastream, detecting one or more cardiac cycles in the data stream, andcertifying the detected cardiac cycles by removing noise and/oroverdetection (such as circuitry and or programming instructionsrepresented in FIG. 11, blocks 552, 560, 570, for example); and whereinthe first analyzer means, second analyzer means, and third analyzermeans are configured to operate in parallel; and wherein the operationalcircuitry further comprises: a first means for comparing detectedcardiac cycles in each of the first, second and third data streams priorto the certification steps for each respective data stream, to identifyone or more of likely noise or overdetection (such as circuitry and orprogramming instructions represented in FIG. 11, block 564, forexample).

A twenty-first non-limiting example takes the form of a cardiac rhythmmanagement device as in the twentieth non-limiting example, wherein theoperational circuitry further comprises a second means for comparingdetected cardiac cycles in each of the first, second and third datastreams prior to the certification steps for each respective datastream, to identify one or more of likely noise or overdetection (suchas circuitry and or programming instructions represented in FIG. 11,block 564, for example).

A twenty-second non-limiting example takes the form of a cardiac rhythmmanagement device having a least first and second sensing vectors andoperational circuitry for analyzing cardiac signals on at least threedata streams as follows: a first data stream for a signal on the firstsensing vector; a second data stream for a signal on the second sensingvector; and a third data stream for a signal calculated as a combinedsignal generated by combining the first and second sensing vectors;wherein the operational circuitry comprises the following: a firstanalyzer means for analyzing the first data stream by filtering the datastream, detecting one or more cardiac cycles in the data stream, andcertifying the detected cardiac cycles by removing noise and/oroverdetection (such as circuitry and or programming instructionsrepresented in FIG. 11, blocks 552, 560, 570, for example); a secondanalyzer means for analyzing the second data stream by filtering thedata stream, detecting one or more cardiac cycles in the data stream,and certifying the detected cardiac cycles by removing noise and/oroverdetection (such as circuitry and or programming instructionsrepresented in FIG. 11, blocks 552, 560, 570, for example); and a thirdanalyzer means for analyzing the third data stream by filtering the datastream, detecting one or more cardiac cycles in the data stream, andcertifying the detected cardiac cycles by removing noise and/oroverdetection (such as circuitry and or programming instructionsrepresented in FIG. 11, blocks 552, 560, 570, for example); and whereinthe first analyzer means, second analyzer means, and means analyzermeans are configured to operate in parallel; and wherein the operationalcircuitry further comprises the following: means for comparing detectedcardiac cycles in each of the first, second and third data streams afterthe certification steps for each respective data stream, to identify oneor more of likely noise or overdetection (such as circuitry and orprogramming instructions represented in FIG. 11, block 564, forexample).

A twenty-third non-limiting example takes the form of a cardiac rhythmmanagement device having a least a first sensing vector and operationalcircuitry for analyzing cardiac signals on at least two data streams,the operational circuitry comprising: receiver means for receiving asignal from the first sensing vector; in a first data stream, a firstmeans for applying a first filtering criteria to the signal from thefirst sensing vector (such as circuitry and or programming instructionsrepresented in FIG. 16, block 760, for example); in a second datastream, a second means for applying a second filtering criteriadifferent from the first filtering criteria (such as circuitry and orprogramming instructions represented in FIG. 16, block 762, forexample); means for combining the first and second data streams togetherto create a series of combined sample points for the cardiac signal eachhaving an amplitude determined at least partly from each of the firstand second data streams; means for performing cardiac cycle detection onthe series of combined sample points (wherein the combined data streamis represented by signal 752 in FIG. 16, and operational circuitry formaking such a signal are described in association therewith).

A twenty-fourth non-limiting example takes the form of a cardiac rhythmmanagement device as in the twenty-third non-limiting example whereinthe operational circuitry includes means for correcting for phasedifferences between the first and second data stream prior to or as partof combining the first and second data streams together (such ascircuitry and/or programming instructions indicated in block 802 of FIG.18).

A twenty-fifth non-limiting example takes the form of a cardiac rhythmmanagement device as in the twenty-third or twenty-fourth non-limitingexamples wherein each of the combined sample points is generated byadding data from the first data stream to data from the second datastream.

A twenty-sixth non-limiting example takes the form of a cardiac rhythmmanagement device as in the twenty-third or twenty-fourth non-limitingexamples wherein each of the combined sample points is generated byadding weighted data from the first data stream to weighted data fromthe second data stream.

A twenty-seventh non-limiting example takes the form of a cardiac rhythmmanagement device as in the twenty-third or twenty-fourth non-limitingexamples wherein the combined sample points are combined together byaddition during a first time period, and by subtraction during a secondtime period, of a cardiac cycle.

A twenty-eighth non-limiting example takes the form of a cardiac rhythmmanagement device having a least first and second sensing vectors andoperational circuitry for analyzing cardiac signals on at least two datastreams as follows: a first data stream for a signal on the firstsensing vector (such as to circuitry and/or programming instructionsrepresented at block 900 in FIG. 20); and a second data stream for asignal on the second sensing vector (such as to circuitry and/orprogramming instructions represented at block 902 in FIG. 20); whereinthe operational circuitry comprises the following: a first detectormeans for detecting first cardiac cycles on the first data stream (suchas to circuitry and/or programming instructions represented at block 900in FIG. 20); a second detector means for detecting second cardiac cycleson the second data stream (such as to circuitry and/or programminginstructions represented at block 902 in FIG. 20); means for determiningwhether an alignment of the first and second cardiac cycles occurs andfinding that alignment has taken place (such as circuitry and/orprogramming instructions represented at block 904 in FIG. 20); means forobserving timing of cardiac cycle detections (such as circuitry and/orprogramming instructions represented at block 908 in FIG. 20) and, if aspurious detection occurs in the first data stream but not the seconddata stream, declaring the spurious detection to be one of overdetectedor noise (such as circuitry and/or programming instructions representedat block 914 in FIG. 20).

A twenty-ninth non-limiting example takes the form of a cardiac rhythmmanagement device as in the twenty-eighth non-limiting example whereinthe operational circuitry includes means for finding that alignmenttakes place by determining an offset between detection of cardiac cyclesin the first data stream and detection of cardiac cycles in the seconddata stream (such as circuitry and/or programming instructionsrepresented at block 908 in FIG. 20).

Each of the first to twenty-ninth non-limiting examples may take theform of an implantable cardiac rhythm management device having therapydelivery capability for delivering therapy in response to detectedtreatable arrhythmia or other condition.

Each of the first to twenty-ninth non-limiting examples may instead takethe form of an implantable cardiac monitoring apparatus.

Each of the first to twenty-ninth non-limiting examples may instead takethe form of a wearable apparatus, with or without therapy capability.

Each of these non-limiting examples can stand on its own, or can becombined in various permutations or combinations with one or more of theother examples.

The above detailed description includes references to the accompanyingdrawings, which form a part of the detailed description. The drawingsshow, by way of illustration, specific embodiments in which theinvention can be practiced. These embodiments are also referred toherein as “examples.” Such examples can include elements in addition tothose shown or described. However, the present inventors alsocontemplate examples in which only those elements shown or described areprovided. Moreover, the present inventors also contemplate examplesusing any combination or permutation of those elements shown ordescribed (or one or more aspects thereof), either with respect to aparticular example (or one or more aspects thereof), or with respect toother examples (or one or more aspects thereof) shown or describedherein.

In the event of inconsistent usages between this document and anydocuments so incorporated by reference, the usage in this documentcontrols.

In this document, the terms “a” or “an” are used, as is common in patentdocuments, to include one or more than one, independent of any otherinstances or usages of “at least one” or “one or more.” Moreover, in thefollowing claims, the terms “first,” “second,” and “third,” etc. areused merely as labels, and are not intended to impose numericalrequirements on their objects.

Method examples described herein can be machine or computer-implementedat least in part. Some examples can include a computer-readable mediumor machine-readable medium encoded with instructions operable toconfigure an electronic device to perform methods as described in theabove examples. An implementation of such methods can include code, suchas microcode, assembly language code, a higher-level language code, orthe like. Such code can include computer readable instructions forperforming various methods. The code may form portions of computerprogram products. Further, in an example, the code can be tangiblystored on one or more volatile, non-transitory, or non-volatile tangiblecomputer-readable media, such as during execution or at other times.Examples of these tangible computer-readable media can include, but arenot limited to, hard disks, removable magnetic or optical disks,magnetic cassettes, memory cards or sticks, random access memories(RAMs), read only memories (ROMs), and the like.

The above description is intended to be illustrative, and notrestrictive. For example, the above-described examples (or one or moreaspects thereof) may be used in combination with each other. Otherembodiments can be used, such as by one of ordinary skill in the artupon reviewing the above description.

The Abstract is provided to comply with 37 C.F.R. §1.72(b), to allow thereader to quickly ascertain the nature of the technical disclosure. Itis submitted with the understanding that it will not be used tointerpret or limit the scope or meaning of the claims.

Also, in the above Detailed Description, various features may be groupedtogether to streamline the disclosure. This should not be interpreted asintending that an unclaimed disclosed feature is essential to any claim.Rather, inventive subject matter may lie in less than all features of aparticular disclosed embodiment. Thus, the following claims are herebyincorporated into the Detailed Description as examples or embodiments,with each claim standing on its own as a separate embodiment, and it iscontemplated that such embodiments can be combined with each other invarious combinations or permutations. The scope of the invention shouldbe determined with reference to the appended claims, along with the fullscope of equivalents to which such claims are entitled.

What is claimed is:
 1. A cardiac rhythm management device havingoperational circuitry for analyzing cardiac signals using a least firstand second cardiac sensing vectors and first and second sensingchannels, wherein the operational circuitry is configured to combine thefirst and second cardiac signals as follows: calculating at least firstand second weighting factors for the at least first and second sensingvectors; applying the first weighting factor to modify signals sensedwith the first sensing vector; applying the second weighting factor tomodify signals sensed with the second sensing vector; combining thesignals from the first and second sensing vectors, as modified by theweighting factors, together for analysis to detect cardiac cycles; andon a triggered or continuous basis, recalculating the weighting factors.2. The device of claim 1 wherein the operational circuitry is configuredto calculate a phase factor to apply to delay one of the first or secondcardiac signal vectors for the combining step.
 3. The device of claim 1wherein the operational circuitry is configured to apply filtering tothe first and second sensing vectors prior to applying the weightingfactors.
 4. The device of claim 1 wherein the operational circuitry isconfigured to apply filtering to the first and second signals asmodified by the weighting factors.
 5. The device of claim 1 furthercomprising: combining the signals from the first and second sensingvectors together, as multiplied by the weighting factors to yield acombined signal; and sampling the combined signal for use in cardiaccycle detection.
 6. The device of claim 1 wherein the operationalcircuitry is configured to perform parallel processing of at least firstand second sampled and conditioned data streams, wherein the first datastream comes from one of the at least first and second sensing vectors,as modified by the weighting factors, and the second data stream comesfrom a combined signal of the first and second sensing vectors.
 7. Thedevice of claim 6 wherein operational circuitry is configured forswitching the first data stream between the first and second sensingvectors, wherein the operational circuitry is further configured toanalyze the first data stream to update one or more of the weightingfactors over time.
 8. The device of claim 7 wherein the operationalcircuitry is further configured to: periodically switch from the firstsensing vector to the second sensing vector for analysis in the seconddata stream at predefined intervals; and occasionally switch from thefirst sensing vector to the second sensing vector for analysis in thesecond data stream in response to a triggering event.
 9. The device ofclaim 6 wherein the operational circuitry is configured to analyze thefirst and second data streams for noise and if noise is found in thefirst data stream but not in the second data stream, modify acorresponding weighting value for whichever of the sense vectors is inthe first data stream at the time of the noise to underweight that datastream.
 10. The device of claim 1 wherein the operational circuitry isconfigured such that: the weighting factors are comprised of an orderedseries of individual weighting multipliers having at least first andsecond values; the step of applying the weighting factors is performedby determining that a new cardiac cycle has been detected, and thenbeginning with a first of the ordered series of individual weightingmultipliers, multiplying the weighting multipliers by individual signalsamples from the sensing vector; and the weighting factors vary inweight from one another by having those which are applied first in timebe of less weight than those applied later in time.
 11. A cardiac rhythmmanagement device having operational circuitry for analyzing cardiacsignals including a least first and second cardiac sensing vectors andfirst and second sensing channels, wherein the operational circuitry isconfigured to combine the first and second cardiac signals as follows:converting data from the at least first and second cardiac sensingvectors into one of spherical and cylindrical coordinates; generating ascalar output from the at least one of spherical and cylindricalcoordinates; performing analysis to detect cardiac cycles using thescalar output; retaining one or more components of the special orcylindrical coordinates to use in addition to the scalar output foridentifying overdetection resulting in the step of performing analysisto detect cardiac cycles using the scalar output.
 12. The device ofclaim 11 wherein the operational circuitry is configured to apply atransformation to a set of data received using the at least first andsecond cardiac sensing vectors, wherein the transformation is generatedby obtaining a normalized data transform to a frame of reference for apatient receiving the cardiac rhythm management device.
 13. The deviceof claim 11 wherein the operational circuitry is configured to act uponthe components of the converted spherical or cylindrical coordinates byapplying a first filtering ruleset to a first data stream, and byapplying a second filtering ruleset to a second data stream, andcombining results of the filtering of each of the first and second datastreams.
 14. A method for combining a first and a second cardiac signalfrom a cardiac rhythm management device having operational circuitry foranalyzing cardiac signals using a least first and second cardiac sensingvectors and first and second sensing channels, the method comprising:calculating at least first and second weighting factors for the at leastfirst and second sensing vectors; applying the first weighting factor tomodify signals sensed with the first sensing vector; applying the secondweighting factor to modify signals sensed with the second sensingvector; combining the signals from the first and second sensing vectors,as modified by the weighting factors, together for analysis to detectcardiac cycles; and on a triggered or continuous basis, recalculatingthe weighting factors.
 15. The method of claim 14 further comprisingcalculating a phase factor to apply to delay one of the first or secondcardiac signal vectors for the combining step.
 16. The method of claim14 further comprising combining the signals from the first and secondsensing vectors together, as multiplied by the weighting factors toyield a combined signal; and sampling the combined signal for use incardiac cycle detection.
 17. The method of claim 14 further comprisingperforming parallel processing of at least first and second sampled andconditioned data streams, wherein the first data stream comes from oneof the at least first and second sensing vectors, as modified by theweighting factors, and the second data stream comes from a combinedsignal of the first and second sensing vectors.
 18. The method of claim17 further comprising: switching the first data stream between the firstand second sensing vectors; analyzing the first data stream to updateone or more of the weighting factors over time; periodically switchingfrom the first sensing vector to the second sensing vector for analysisin the second data stream at predefined intervals; and occasionallyswitching from the first sensing vector to the second sensing vector foranalysis in the second data stream in response to a triggering event.19. The method of claim 17 further comprising analyzing analyze thefirst and second data streams for noise and if noise is found in thefirst data stream but not in the second data stream, modifying acorresponding weighting value for whichever of the sense vectors is inthe first data stream at the time of the noise to underweight that datastream.
 20. The method of claim 14 wherein: the weighting factors arecomprised of an ordered series of individual weighting multipliershaving at least first and second values; the step of applying theweighting factors is performed by determining that a new cardiac cyclehas been detected, and then beginning with a first of the ordered seriesof individual weighting multipliers, multiplying the weightingmultipliers by individual signal samples from the sensing vector; andthe weighting factors vary in weight from one another by having thosewhich are applied first in time be of less weight than those appliedlater in time.